[PATCH v2 1/4] timer: Optimize fastpath_timer_check()

Jason Low
2015-10-14T19:07:58Z

In fastpath_timer_check(), the task_cputime() function is always
called to compute the utime and stime values. However, this is not
necessary if there are no per-thread timers to check for. This patch
modifies the code such that we compute the task_cputime values only
when there are per-thread timers set.

Signed-off-by: Jason Low <jason.low2@hp.com>
Reviewed-by: Oleg Nesterov <oleg@redhat.com>
Reviewed-by: Frederic Weisbecker <fweisbec@gmail.com>
Reviewed-by: Davidlohr Bueso <dave@stgolabs.net>
---
kernel/time/posix-cpu-timers.c | 11 +++--------
1 files changed, 3 insertions(+), 8 deletions(-)

diff --git a/kernel/time/posix-cpu-timers.c b/kernel/time/posix-cpu-timers.c
index 892e3da..aa4b6f4 100644
--- a/kernel/time/posix-cpu-timers.c
+++ b/kernel/time/posix-cpu-timers.c
@@ -1117,17 +1117,12 @@ static inline int task_cputime_expired(const struct task_cputime *sample,
static inline int fastpath_timer_check(struct task_struct *tsk)
{
struct signal_struct *sig;
- cputime_t utime, stime;
-
- task_cputime(tsk, &utime, &stime);

if (!task_cputime_zero(&tsk->cputime_expires)) {
- struct task_cputime task_sample = {
- .utime = utime,
- .stime = stime,
- .sum_exec_runtime = tsk->se.sum_exec_runtime
- };
+ struct task_cputime task_sample;

+ task_cputime(tsk, &task_sample.utime, &task_sample.stime);
+ task_sample.sum_exec_runtime = tsk->se.sum_exec_runtime;
if (task_cputime_expired(&task_sample, &tsk->cputime_expires))
return 1;
}
--
1.7.2.5